An integrated single-switch approach to improve harmonic performance of standard PWM adjustable speed drives

In this paper, an integrated single-switch approach to improve the harmonic performance of standard PWM adjustable speed drives (ASD) is presented. The approach is essentially an add-on solution to a standard ASD topology. The approach is based on circulating a third harmonic current to reduce the harmonics of the line current. The dynamic braking chopper available in standard ASDs is used to control the amplitude of the third harmonic circulating current. Analysis, design and simulations are presented to determine the performance of the proposed scheme with different line impedances and with and without DC-link inductance in the ASD. Utility input current distortion well below 15% is obtained. This paper also presents how this new approach is capable of reducing the harmonic distortion in multiple drives. The paper includes experimental results using a 480 V, 10 kW commercial adjustable speed drive retrofitted with the proposed approach.